Composite Materials V

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Authors: Cong Fa Zhang, Wei Cao, Tong Xiang Fan, Di Zhang
Abstract: Alloying additions have an important effect on in-situ chemical reaction 4Al+Si3N4=4AlN+3Si to synthesis (AlN+Mg2Si)/Mg composites. Using the Wilson equation and an extended Miedema model, the activity in a multiple-component system can be calculated,and then the Gibbs free energy can be calculated. In final, the influence of alloying element additions on the in-situ chemical reaction at high temperature is investigated from a thermodynamic viewpoint.
Authors: Wei Cao, Cong Fa Zhang, Tong Xiang Fan, Di Zhang
Abstract: The effect of the alloying element additions on in-situ chemical reaction to synthesize particulate reinforced TiC/Mg composites was evaluated from the viewpoint of thermodynamics. The influences of alloying elements on the changes of the activity coefficient and the excess free energy in molten magnesium were calculated. The results show that additions, such as Nd, La, Ca, Cu and Zr can promote TiC formation, at the same time hinder the brittle TiAl3 phase formation.
Authors: Wei Cao, Cong Fa Zhang, Tong Xiang Fan, Di Zhang
Abstract: TiB2 particulate reinforced magnesium matrix composites were successfully fabricated by adding a TiB2–Al master alloy processed via the flux-assisted synthesis (FAS) reaction into molten magnesium. X-ray diffraction (XRD) analysis and microstructural characterization of the TiB2–Al master alloy revealed the formation and uniform distribution of TiB2 reinforcements. By stirring, magnesium matrix composites with dispersed homogenously TiB2 particles can be obtained. Microstructural characterization of the TiB2/Mg composites revealed retention of hexagonal or rectangular TiB2 particulates with the size of about 1 μm.
Authors: Yan Bing Wang, Zhi Xiong Huang, Yan Qin, Ming Du, Lian Meng Zhang
Abstract: In this paper, a three-phase composite with electrically conductive carbon black (ECCB) and piezoelectric ceramic particles, PMN, embedded into butyl (PMN/ECCB/IIR) was prepared by simple blend and mold-press process. Dynamic mechanical properties with various ECCB loading were tested by dynamic mechanical analysis (DMA). DMA shows that the ECCB loading has remarkable effect on the dynamic mechanical properties of the three-phase composite. The temperature range of loss factor (tanδ) above 0.3 the composite was broadened by almost 100°C and the maximum of loss factor shifts to higher temperature in the testing temperature range respectively with increasing the ECCB loading. The piezoelectric damping theory was used to explain the experimental results. The three-phase composites with proper composition can be used as high damping polymer materials.
Authors: Fa Qiang Yan, Fei Chen, Qiang Shen, Lian Meng Zhang
Abstract: In the present study, α-Si3N4 is prepared by using MgO and Al2O3 as the sintering additives and spark plasma sintering (SPS) technique. The SPS sintering mechanism is discussed. The relationship between the content of sintering additives, sintering temperature and relative densities of the samples is analyzed. The results suggest that when the sintering temperature is 1300-1500°C, the content of sintering additives is 6wt.%-10wt.%, the relative density of sintered samples is 64%-96%. When the sintering temperature reaches 1400°C, the content of sintering additives is 10%, the samples can be fully dense sintered and the relative density can be up to 95%. The sintering mechanism is liquid phase sintering. The bending strength of the sintered samples is 50-403MPa and has a close correlation with the relative density.
Authors: Chang Lian Chen, Qiang Shen, Jun Guo Li, Lian Meng Zhang
Abstract: A series of zirconia porous ceramics with different density are fabricated with commercial zirconia powder and zirconia hollow balls by pressureless sintering technology. The microstructure and phase transformation are characterized respectively by SEM and XRD testing methods. The result indicates that the density and compressive strength depend greatly on zirconia powder content at the same sintering temperature, and elevating sintering temperature just has a little effect on the density and compressive strength for the samples of the same zirconia powder content. The XRD diffraction patterns analysis shows that elevating sintering temperature is helpful to eliminate monoclinic zirconia and the best sintering temperature should be beyond 1700°C.
Authors: Zu Sheng Zhan, Yan Sheng Gong, Qiang Shen, Lian Meng Zhang
Abstract: Potassium lithium niobate (KLN: K3Li2Nb5O15) films have been deposited on quartz glass by Pulsed laser deposition (PLD) technique using a stoichiometric KLN target as starting materials. By investigating the effects of both the oxygen pressure and the substrate temperature on the structure of KLN films, optimum parameters have been identified for the growth of high-quality KLN films. At 10Pa oxygen ambient pressure, tetragonal tungsten-bronze-type structure of KLN films with (310) preferred orientation can be achieved at substrate temperatures in the range of 700-800°C. Optical studies indicate that the films are highly transparent in the visible-near-infrared wavelength range.
Authors: K. Wang, Zheng Yi Fu, Wei Min Wang, Yu Cheng Wang, H. Wang, Jin Yong Zhang, Qing Jie Zhang
Abstract: Combustion synthesis of titanium diboride(TiB2) from titanium(Ti) and boron(B) powders was studied by theoretical calculation and experimental analysis. In high temperature range or in low temperature range, the calculated activation energies are 140KJ/mol or 355KJ/mol respectively, which is described by a change from dissolution-precipitation controlled process to diffusion-controlled process. With the increase of particle size of the raw materials, combustion temperature and propagating rate will both reduce. The propagating rate decreases with the addition of diluents. Further increase of diluents may result in a stop of the combustion wave halfway or even a failure of ignition.
Authors: Cun Zhu Nie, Jia Jun Gu, Jun Liang Liu, Di Zhang
Abstract: The microstructures and tensile performance of B4C particulate reinforced 2024 Al alloy matrix composites produced by mechanical alloying and common blending techniques were investigated. The results showed that mechanical alloying was an effective way to fabricate the particulate reinforced Al matrix composites over common blending. The samples by different mixing techniques exhibited a clean and chemical products free interface. Tensile strength and elastic modulus of the composites was higher than that of the based alloy at the expense of ductility. The composites by common blending exhibited a more ductile fracture surface in contrast to specimen by mechanical alloying.
Authors: Jun Qiang Lu, Wei Jie Lu, Yang Liu, Ji Ning Qin, Di Zhang
Abstract: In this paper, Ti-6Al-4V matrix composites reinforced with 5% or 10% TiB and TiC were in situ synthesized by common casting and hot-forging technology utilizing the reaction between titanium and B4C. The phase constituents were identified by XRD while transus temperatures were determined by DSC and metallography. The evolution of microstructures was studied by optical microscopy. The effects of reinforcements on the microstructures, tensile properties and fractures at room temperature were discussed. The results show that yield strength and ultimate tensile strength increased significantly while ductility decreased with reinforcements increasing. Fracture type turned to brittle when reinforcements increased.

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